Method of and apparatus for abrading outer peripheral parts of a semiconductor wafer

ABSTRACT

The invention provides a method of and an apparatus for abrading outer peripheral parts of a semiconductor wafer having a protective sheet adhesively attached to its surface where semiconductor elements are formed. The semiconductor wafer is held horizontally and an abrading tape held inside an abrading head is run and pressed against the outer peripheral part of the semiconductor wafer. The abrading tape has abrading particles attached to a base sheet by electrostatic spraying.

This application is a continuation of International Application No.PCT/JP2009/52717, filed Feb. 17, 2009 which claims priority on JapanesePatent Application 2008-42174 filed Feb. 22, 2008.

BACKGROUND OF THE INVENTION

This invention relates to a method of abrading outer peripheral parts ofa semiconductor wafer and an apparatus therefor, and more particularlyto a method of abrading outer peripheral parts of a semiconductor waferto be carried out prior to the so-called back-grinding process in whichthe front surface of a semiconductor wafer having semiconductor elementsand electronic components formed on its front surface is abraded forreducing its thickness and an apparatus therefor.

Semiconductor wafers go through each of many processes such as the filmforming process, the surface fabricating process and the washing processduring their production process for forming semiconductor elements andelectronic components. During this process, outer peripheral parts ofthe semiconductor wafers are subjected to a chamfering process in orderto prevent them from becoming cracked or chipped.

The chamfering process of outer peripheral parts of a semiconductorwafer is explained with reference to FIG. 6 for showing theback-grinding process. As shown in FIG. 6A which is a plan view of asemiconductor wafer 11 and FIG. 6B which is an enlarged sectional viewtaken along line 6B-6B indicated in FIG. 6A, the semiconductor wafer 11has an external peripheral part 13 which is of the shape of an arc (orR-shape) because a chamfering process has been carried for making theperipheral part 13 in an arcuate shape.

After the film which has been formed by each of the processes reachesthe outer peripheral part, portions of the film thus formed on the outerperipheral part and the objects which have become attached by theseprocesses are removed by means of a grindstone or an abrading tape, andthe production process of the semiconductor wafer is continued while acleaning process is carried out, as explained, for example, in JapanesePatent Publications Tokkai 06-104228, 07-205001, 2002-025952 and2005-007518.

In this process described above, a abrading tape was conventionally usedfor the finishing process after a chamfering process is completed with agrindstone into an arcuate shape. The abrading tape used for thispurpose is usually of a type generally produced by coating.

The semiconductor wafers having semiconductor elements and electroniccomponents thus formed on their surfaces in the production processdescribed above are divided into individual chips by a dicing processafter an electric inspection is carried out.

In response to the recent demands for smaller and lighter electronicapparatus and devices, chips are now required to be formed with anextremely small thickness such as 100 μm or less and even 50 μm or less.It is for this reason that the back-grinding process has come to becarried out for reducing the thickness of semiconductor wafers byabrading its back surface 14 before the dicing process is carried out todivide the semiconductor wafers with semiconductor elements andelectronic components formed on their surfaces to divide them intoindividual chips.

In this back-grinding process, as shown in FIG. 6B, for example, asemiconductor wafer 11 having semiconductor elements and electroniccomponents formed thereon is horizontally fastened to a holder (notshown) with its front surface 15 facing downward as its back surface 14is subjected to an abrading process. The semiconductor wafer 11 isfastened to the holder after a protective sheet 12 is attached to thefront surface 15 of the semiconductor wafer 11 in order to prevent thesemiconductor elements and the electronic components formed on thisfront surface 15 from becoming contaminated or damaged.

The semiconductor wafer 11, thus prepared, is worked upon on its backsurface 14 with an abrading grindstone (such as a cup-shaped grindstone)to a specified thickness. In the case of a very small final thickness,the semiconductor wafer may have to be abraded such that more than ahalf of its original thickness will be removed. For example, asemiconductor wafer may have to be abraded from the original thicknessof 1 mm-0.7 mm down to the final thickness of 100 μm-50 μm.

If the back surface 14 of the semiconductor wafer 11 as shown in FIG. 6Bis abraded, its originally R-shaped peripheral part 13 gradually becomesan acute angular shape 13′, as shown in FIG. 6C after the back-grindingprocess. Such a change into a knife-edge shape becomes more prominent asthe semiconductor wafer is made thinner. As the thickness of thesemiconductor wafer is further reduced, its strength against breakagealso becomes reduced. For this reason, the acute angular edge part 13′of the semiconductor wafer is easily chipped by the load of theback-grinding process or an impulse applied at a later processthereupon. Such defects and chipping may tend to serve as a trigger tomake the semiconductor wafer easily breakable.

In view of this problem, it has become a common practice to employ agrindstone in an abrading process in order to remove the R-shapedperipheral parts of the semiconductor wafer with the protective sheetattached thereto prior to the back-grinding process such that aknife-edge shape will not result.

By such a method as described above, however, the protective sheetbecomes abraded as outer peripheral parts of the semiconductor wafer areabraded to remove the chamfered parts if the protective sheet is cutnear the outer periphery of the semiconductor wafer. If the resinmaterial of the protective sheet becomes attached to the abradingparticles of the grindstone and the grindstone becomes clogged, the workefficiency and the quality of the product are adversely affected and thesemiconductor wafer may become damaged.

In view of the above, new abrading methods are being proposed for theouter peripheral parts of a wafer in order to eliminate the problemscaused by the attachment of the protective sheet material onto theabrading grindstone, as disclosed, for example, in Japanese PatentPublications Tokkai 2003-273053, 2005-093882 and 2007-042811, includinga method of using a protective sheet with a diameter smaller than thatof the semiconductor wafer (within the outer peripheral abrading area)and thereafter abrading the outer peripheral parts of the semiconductorwafer.

These prior art methods, however, require complicated steps of detectingand adjusting the accuracy in the pasting of the protective sheet thatadversely affects the work efficiency. Abrading by a grindstone,furthermore, requires frequent dressing of the grindstone because itsclogging adversely affects the quality of the abraded product even if noprotective sheet is employed. Moreover, the mechanical accuracy,rigidity and structure of the abrading apparatus become complicated, themaintenance problems become involved, and some associated equipments maybe required.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a method of andan apparatus for abrading outer peripheral parts of a semiconductorwafer capable of preventing the outer peripheral parts of thesemiconductor wafer to take upon the shape of a knife edge by theback-grinding process, not influenced by the position of pasting theprotective sheet, not having the problem of clogging at the time ofabrading with the protective sheet, and capable of forming the abradedsurface continuously on the outer peripheral parts approximatelyperpendicularly.

In view of the object described above, the present invention provides amethod of abrading outer peripheral parts of a semiconductor waferhaving a front surface on which semiconductor elements are formed and aprotective sheet is adhesively attached, the method comprising the stepsof holding the semiconductor wafer such that its front surface ishorizontal and causing an abrading tape mounted inside an abrading headto run and pressing the abrading tape against and thereby abrading anouter peripheral part of the semiconductor wafer, wherein the abradingtape has abrading particles attached thereto by electrostatic spraying.

Since outer peripheral parts of a semiconductor wafer are thus abradedwhile an abrading tape is caused to run, it becomes easier to carry outthe process by following the rotary vibrations of the semiconductorwafer and the changes in the shape of the semiconductor wafer itselfwithout the influence by the rotary axis of the semiconductor wafer (orthe accuracy of its centering), unlike by a conventional abrading methodwith a grindstone (cut-out sizing method), and it becomes possible toprevent the chipping and generation of defects on the outer peripheralparts of semiconductor wafers. The structure of the required apparatusalso becomes simpler because the mechanical accuracy, rigidity andstructure required of the apparatus become less influential.

Moreover, since the abrading tape is constantly being run, a freshabrading part is always being supplied and hence there is no problem ofclogging although the protective sheet is abraded at the same time andthe abrasion can be effected dependably and at a high efficiency. As aresult, it becomes possible to abrade the outer peripheral parts of asemiconductor wafer together with its protective sheet.

The abrading tape is produced by having abrading particles attached byelectrostatic spraying. Tapes having abrading particles attached on abinder resin layer by electrostatic spraying have less unwanted resinlayer on the surface of the abrading particles. Since the cutting edgesof the abrading particles are sharp, high-speed processing is possible.Since these cutting edges cut well, the end surface of the processedsemiconductor wafer tends to chip less.

In the above, “electrostatic spraying” means spreading abradingparticles by electrostatically charging them. Since the abradingparticles thus spread by electrostatic spraying are scattered whilebeing mutually repelled electrostatically, they do not form anyagglomerations and can be spread out uniformly.

The abrading tape is caused to run horizontally or vertically whilebeing pressed against an outer peripheral part of the semiconductorwafer.

The abrading tape mounted inside the abrading head is pressed againstand caused to abrade the semiconductor wafer while the tape surface issloped by an angle of 10° or less from the vertical direction. Thesloping may be either forward or backward and is an effective methodwhen the upper portion or a lower portion of an outer peripheral part ofthe semiconductor wafer is abraded. In this way, the tip end portion ofthe outer peripheral part of the semiconductor wafer can be abradedeffectively.

If the tip end portion is abraded by forwardly sloping the abradingsurface of the abrading tape inside the abrading head with respect tothe front surface of the semiconductor wafer by an angle of 10° or lessfrom the vertical direction, for example, the outer peripheral part ofthe semiconductor wafer becomes an obtuse angle or a nearly obtuse angleat the time of back-grinding, chipping becomes unlikely to take place onthe tip end portion. If the slope angle is made greater than 10°, thetip end portion becomes like a sharp knife edge and it becomes easier toform defects and cracks while it is being transported during theabrading process or during a later process. This is why it is preferableto make the angle of the slope equal to or less than 10°. The angle ofthe slope should be 10° or less, whether the abrading head is inclinedforward or backward from the vertical direction.

The diameter of the abrading particles on the abrading tape shouldpreferably be in the range of #600 or 30 μm to #3000 or 5 μm. If it isless than #600, chipping will be increased. If it is over #3000, thespeed of processing is reduced and the process efficiency is adverselyaffected.

The abrading process is preferably carried out while an abrading liquidis supplied.

The pad at the tip of the holding guide is preferably comprised of anelastic material having shore-A hardness in the range of 20-50°. Such anelastic material is capable of absorbing mechanical vibrations, preventsgeneration of detects and serves to stabilize the shape of the abradedsurface of the semiconductor wafer and to reduce the generation ofchipping.

It is also preferable to form at least the contact surface of the pad atthe tip with a lubricating material with lubricity. It is preferable touse a pad material with lubricity in order to allow the abrading tape torun smoothly since the back surface of the abrading tape is pressed bythe pad.

The invention also relates to an abrading apparatus for abrading outerperipheral parts of a semiconductor wafer having a front surface onwhich semiconductor elements are formed and a protective sheet isadhesively attached, comprising holding means for holding thesemiconductor wafer such that its front surface is horizontal and anabrading head containing therein an abrading tape which is adapted torun and to abrade an outer peripheral part of the semiconductor waferbeing held by the holding means, wherein the abrading tape has abradingparticles attached thereto by electrostatic spraying.

With an abrading apparatus thus structured, the outer peripheral partsof a semiconductor wafer fabricated in the shape of an arc (or R-shape)can be abraded nearly perpendicularly and hence the outer peripheralparts do not take on the shape of a knife edge. Thus, although aback-grinding process is carried out thereafter, it is possible toprevent the generation of breakage, cracks and defects.

Since outer peripheral parts of a semiconductor wafer are thus abradedwhile an abrading tape is caused to run, it becomes easier to carry outthe process by following the rotary vibrations of the semiconductorwafer and the changes in the shape of the semiconductor wafer itselfwithout the influence of the rotary axis of the semiconductor wafer (orthe accuracy of its centering), unlike by a conventional abrading methodwith a grindstone (cut-out sizing method), and it becomes possible toprevent the chipping and generation of defects on the outer peripheralparts of semiconductor wafers. The structure of the required apparatusalso becomes simpler because the mechanical accuracy, rigidity andstructure required of the apparatus become less influential.

Since use is made of an abrading tape produced by having abradingparticles attached by electrostatic spraying, there is less unwantedresin layer on the surface of the abrading particles than ordinarilyused tapes of the type produced by coating. Since the cutting edges ofthe abrading particles are sharp, high-speed processing is possible.Since these cutting edges cut well, the end surface of the processedsemiconductor wafer tends to chip less.

With an abrading apparatus according to this invention, outer peripheralparts of a semiconductor wafer can be abraded together with theprotective sheet thereon. Since the abrading tape is constantly beingrun, a fresh abrading part is always being supplied and hence there isno problem of clogging although the protective sheet is abraded at thesame time, and the abrasion can be effected dependably and with a highefficiency.

The abrading tape is preferably arranged to travel vertically orhorizontally as it contacts the outer peripheral part of thesemiconductor wafer. If the abrading tape is thus arranged to travelvertically or horizontally, the outer peripheral parts of thesemiconductor wafer can be abraded approximately perpendicularly andsince a new portion is being supplied constantly, the abrading processcan be executed with a high efficiency without the problem of clogging.

The abrading head comprises a holding guide for pressing the abradingtape against the outer peripheral part and a compressing mechanism forpressing this holding guide. Since the abrading tape, too, can thusadjust the compressive force, the abrading process can be carried outefficiently and uniformly.

The abrading head further comprises a pressing position adjustingmechanism that rotates the holding guide in a radial direction of thesemiconductor wafer, the pressing position adjusting mechanismcomprising a rotary arm that undergoes a rotary motion with the holdingguide mounted thereto, a shaft that is connected to the rotary arm and adriving device that is connected to and transmits a torque for therotary motion to the shaft and the abrading head preferably serving tocontrol the torque by the driving device to adjust the rotary positionwhere the abrading tape is pressed by the holding guide onto the outerperipheral part of the semiconductor wafer.

Since the rotary position of the abrading tape pressed against theholding guide is adjusted as the rotary position of the rotary armhaving the holding guide attached thereto is varied, the contactposition, the angle of contact and the pressure between the outerperipheral part of the semiconductor wafer and the abrading tape can becorrected and hence the accuracy of the abrading process can beimproved.

The present invention makes it possible to reduce damages and cracksgenerated on the outer peripheral parts in the back-grinding process ona semiconductor wafer, as well as damages and cracks after the workingon the back surface.

Unlike the abrading process by means of a grindstone, furthermore, thepresent invention makes it possible to carry out an abrading processwith a high level of accuracy because a fresh abrading past isconstantly being supplied and hence there is no clogging although theprotective sheet is abraded at the same time.

Since the abrading particles are attached to the abrading tape byelectrostatic spraying, there are less unwanted resin layers on thesurface of the abrading particles than in the case of an ordinary tapeof the type produced by coating, and high-speed processing is madepossible since the cutting edges of the abrading particles are sharp.Since the dressing process for the grindstone becomes unnecessary, thework can be carried out efficiently and stably within a short processingtime.

Because there is no effect from the precision of the used apparatus orthe rotary vibrations of the semiconductor wafer, the structure of theapparatus can be simplified and the abrading process can be carried outsmoothly without any abnormal chipping around the entire circumferenceof the semiconductor wafer after the process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view conceptually showing the positional relationshipbetween a semiconductor wafer and an abrading head of an abradingapparatus for outer peripheral parts of a semiconductor wafer accordingto a first embodiment of this invention.

FIG. 2 is a plan view conceptually showing the positional relationshipbetween a semiconductor wafer and an abrading head of an abradingapparatus for outer peripheral parts of a semiconductor wafer accordingto a second embodiment of the invention.

FIGS. 3A, 3B, 3C and 3D, together referred to as FIG. 3, are diagramsfor showing the steps of a method of abrading peripheral parts of asemiconductor wafer according to this invention.

FIG. 4 is a front view of an abrading apparatus for outer peripheralparts of a semiconductor wafer according to this invention.

FIG. 5 is a drawing for explaining the pressure adjusting part of theholding guide 46 shown in FIG. 4.

FIG. 6, comprising FIGS. 6A, 6B and 6C, are drawings for explaining theback-grinding process on a semiconductor wafer.

FIG. 7 is a schematic front view of the pressing position adjustingmechanism.

FIG. 8 includes FIGS. 8A and 8B, FIG. 8A being a schematic side view ofthe pressing position adjusting mechanism before it is pressed againstthe outer peripheral part of a semiconductor wafer, and FIG. 8B being aschematic side view of the pressing position adjusting mechanism when itis pressed against the outer peripheral part of the semiconductor wafer.

DETAILED DESCRIPTION OF THE INVENTION

A abrading method of this invention for outer peripheral parts of asemiconductor is a method that is carried out prior to the back-surfaceabrading process (known as the back-grinding process) of a semiconductorwafer.

The accompanying drawings will now be referenced for explaining apreferred form of the method of this invention of abrading outerperipheral parts of a semiconductor wafer and the apparatus for abradingouter peripheral parts of a semiconductor wafer. In these figures,equivalent or like components will be referred to by the same numeralsor symbols and will not be repetitiously explained.

An abrading apparatus embodying this invention for outer peripheralparts of a semiconductor wafer will be explained first.

FIG. 1 is a front view conceptually showing the positional relationshipbetween a semiconductor wafer and an abrading head of an abradingapparatus according to a first embodiment of this invention for outerperipheral parts of a semiconductor wafer. FIG. 2 is a plan viewconceptually showing the positional relationship between a semiconductorwafer and an abrading head of an abrading apparatus according to asecond embodiment of this invention for outer peripheral parts of asemiconductor wafer. FIGS. 3A, 3B, 3C and 3D, together referred to asFIG. 3, are diagrams for showing the steps of a method according to thisinvention of abrading peripheral parts of a semiconductor wafer. FIG. 4is a front view of an abrading apparatus according to this invention forouter peripheral parts of a semiconductor wafer. FIG. 5 is a drawing forexplaining the pressure adjusting part of the holding guide 46 shown inFIG. 4.

As shown in FIG. 1, the abrading apparatus according to the firstembodiment of this invention for outer peripheral parts of asemiconductor wafer is provided with a rotating mechanism 21 forcarrying a semiconductor wafer 11 horizontally thereon with its backsurface (back-grinding surface) facing upward and rotating it and anabrading head 40 for abrading its outer peripheral parts.

The disk-shaped semiconductor wafer 11 is horizontally placed on aholding table 23, which is supported on a rotary shaft 27 rotatablyattached to a stage 24 and made rotatable by a motor (not shown).

The abrading head 40 is disposed so as to travel in the direction inwhich an abrading tape 20 will advance perpendicularly to the surface ofthe semiconductor wafer 11 which is placed horizontally, that is, in thevertical direction, and the abrading tape 20 is pressed approximatelyperpendicularly to the edge surface of the semiconductor wafer 11.

The abrading tape 20 is contained inside the abrading head 40, beingwound around a feeder reel 42. It is structured such that the abradingtape will be taken up by a take-up reel 43 after passing by an auxiliaryroller 45 a, a lower roller 44 a, an upper roller 44 b and anotherauxiliary roller 45 b.

The abrading tape 20 travels vertically between the lower roller 44 aand the upper roller 44 b to carry out the abrading process as it ispressed against the outer peripheral part of the horizontally placedsemiconductor wafer 11 by a pad 47 which is at the tip of a holdingguide 46 perpendicularly to the abrading tape 20. The holding guide 46serves to press the abrading tape 20 against the outer peripheral partof the semiconductor wafer 11 by being pressed in the direction shown byan arrow 51 with adjustment by means, for example, of an air cylinder.

A nozzle 52 for spraying an abrading liquid is provided at a positionwhere the abrading tape 20 is pressed against the outer peripheral partof the semiconductor wafer 11, and an abrading liquid is spread throughthis nozzle 52 at the time of the abrading process.

According to the first embodiment of the invention described above, theprotective sheet 12 (shown in FIG. 3 as being adhesively attached to thesemiconductor wafer 11) is effectively prevented from becoming peeledoff because the abrading tape 20 runs vertically upward and the abradingprocess can be carried out in the direction of pressing it in thedirection towards the wafer.

Next, FIG. 2 is referenced to explain an abrading apparatus according tothe second embodiment of this invention for outer peripheral parts of asemiconductor wafer.

FIG. 2 is a front view for showing an abrading apparatus according tothe second embodiment of the invention for outer peripheral parts of asemiconductor wafer. Portions thereof that are common to the firstembodiment will not be repetitiously described. Only those portions thatare different will be explained. Equivalent or like components areindicated by the same numerals or symbols as in FIG. 1.

The abrading head 40 according to this embodiment is disposed such thatthe abrading tape 20 will run between the lower roller 44 a and theupper roller 44 b in the circumferential direction of the horizontallyplaced semiconductor wafer 11. In other words, the abrading tape 20 runshorizontally between the lower roller 44 a and the upper roller 44 b. Itis preferable to cause the abrading tape 20 to run opposite to thedirection of rotation of the semiconductor wafer 11 at the positionwhere the abrading tape 20 is pressed against the outer peripheral partof the semiconductor wafer 11.

The second embodiment is advantageous in that the required width of theabrading tape 20 may be reduced, compared to the first embodiment of theinvention. It also has the advantage that the mechanical effects such asthe amplitude of motion in the vertical direction by the rotation of thewafer can be reduced at the time of the abrading process.

The first embodiment and the second embodiment of the inventiondescribed above are different only in that the abrading tape 20 travelsvertically or horizontally between the lower roller 44 a and the upperroller 44 b. If it is so arranged that the abrading head 40 is rotatablesuch that the abrading tape 20 can be made to travel either verticallyor horizontally between the lower roller 44 a and the upper roller 44 b,the features of both the first and second embodiments of the inventioncan be realized.

Next, an abrading method of this invention for abrading outer peripheralparts of a semiconductor wafer is explained. According to this method, aprotective sheet is adhesively attached to a semiconductor wafer withsemiconductor elements and electronic components formed thereupon andthe semiconductor wafer is thereafter placed on the holding table 23shown in FIG. 1 or 2 with its front surface facing downward and its backsurface facing upward.

FIGS. 3A, 3B, 3C and 3D, together referred to as FIG. 3, are diagramsfor showing the steps of a method according to this invention ofabrading peripheral parts of a semiconductor wafer, from the step ofpasting the protective sheet on the wafer until the back-grinding step.

Prior to the start of the process by the abrading method according tothis invention, the protective sheet 12 is adhesively attached, as shownin FIG. 3A, onto the front surface 15 of the semiconductor wafer 11where semiconductor elements and electronic components are alreadyformed.

The protective sheet 12 may be preliminarily cut in the size of theregion according to the external shape of the semiconductor wafer 11 andadhesively attached onto the front surface 15 or may be pasted on thefront surface 15 first and then cut along the outer circumference.

Next, as shown in FIG. 3B, the semiconductor wafer 11 with theprotective sheet 12 pasted thereto is placed on and affixed to theholding table 23 shown in FIG. 1 or 2 with the surface having theprotective sheet 12 facing downward.

Next, the semiconductor wafer 11 is rotated and the abrading tape 20contained inside the abrading head 40 is moved to the side of the outerperipheral part of the semiconductor wafer 11 and the abrading processis carried out by causing the abrading tape 20 to run and be pressedagainst the outer peripheral part of the semiconductor wafer 11. Theabrading tape 20 is pressed from its back side by means of the holdingguide 46. The outer peripheral part of the semiconductor wafer 11 isthus abraded by a required amount and the process is ended at a finalposition.

FIG. 3C shows the sectional shape of the outer peripheral part of thesemiconductor wafer at the end of the abrading process. Since theabrading process can be carried out according to this invention whilethe abrading tape 20 is running, there is no problem of clogging whichmay occur if a grindstone is used, while the protective sheet 12 isabraded at the same time as the external peripheral part 13.

The semiconductor wafer 11 with its outer peripheral parts thus abradedis then subjected to a back-grinding process to have its back surfaceabraded, for example, by a cup-shaped grindstone rotating at a highspeed such that it is thinned, as shown in FIG. 3D, to its finalthickness. Since no sharp knife-edge shape appears after theback-grinding process, as shown in FIG. 3D, the semiconductor wafer isnot easily breakable or chipped.

Next, an abrading tape 20 and a pad 47 according to a preferredembodiment of the invention will be explained.

An abrading tape 20, rather than a abrading tape, is used according tothis invention. Plastic films of polyethylene terephthalate (PET),polyester, polyolefin, EVA resins, polyvinyl carbonate (PVC) orpolyethylene may be used as its base sheet. An abrading tape obtained byforming on the surface of this base sheet an abrading particle layerhaving one or more kinds of abrading particles selected frommicro-particles of carborundum, diamond, aluminum oxide, silica andcerium oxide may be used.

A particularly preferable kind of abrading tape 20 for the purpose ofthis invention may be produced by spreading abrading particles on thesurface of a binder resin with which the surface of the film material iscoated.

Examples of such a binder resin include polyester resins, epoxy resins,acryl resins, urethane resins and silicone resins.

The abrading particles are applied by using the charge spraying methodsuch that directionality can be provided in the distribution of theabrading particles, in contrast to the conventional abrading tapesproduced by a coating method. Since the cutting edges of the abradingparticles can thus be aligned on the surface of the abrading tape, theabrading efficiency can be improved. Since the surface of the abradingparticles is covered by a thin layer of binder resin, furthermore, thereis no problem of these abrading particles dropping off and this alsocontributes to the improvement in the abrading efficiency.

Such an abrading tape 20 may be produced by applying a binder resin tothe surface of a base film material, thereafter ionizing (charging) theabrading particles by a field charging method, a corona dischargingmethod or a frictional charging method, spreading them on the surface ofthe aforementioned binder resin and thereafter hardening the binderresin. The binder resin may be hardened by heating or by the UVhardening method.

The preferable range of the size of the abrading particles is #600-#3000(or 30 μm-5 μm in average diameter). If it is below #600, the generationof chips becomes a problem. If it is over #3000, the work efficiencybecomes deteriorated.

Compared to conventional tapes obtained by coating with a mixture ofabrading particles and a binder, the abrading tapes of this invention asdescribed above have an appropriate degree of directionality in theabrading particles on the surface of the base film material and hencehave a superior abrading efficiency.

As another example having a mixture of abrading particles and a binderresin, abrading tapes 20 with a patterning by roll transcription suchthat the surface has a pointed shape may be used.

As the pad 47 at the tip of the holding guide 46 for pressing theabrading tape 20, on the other hand, an elastic material with shore-Ahardness in the range of 20-50° is used. Examples of such materialinclude resin and rubber materials. Those with a small frictionalresistance against the running abrading tape are preferable.

In the above, shore-A hardness is a standard for measuring the hardnessof rubber by using a durometer (or a spring-type hardness meter forrubber) adapted to insert a probe into the surface of a target object todeform it for measurement and to convert the degree of deformation intoa number (or the depth of deformation) (JIS K6253, Type A) (Method ofPhysical Examinations of Rubber, New JIS Guide, edited by Japan RubberSociety, Aug. 31, 1996, published by Daisei-sha). Shore Durometer Type-AASTM D2240 (trade name, produced by Instron Corporation) may be used.

The abrading tape 20 can be fed smoothly if a lubricating layer isformed with Teflon (trade name) or the like on the surface of the pad 47where the tape is contacted.

If the shore-A hardness is 20° or less, the abrading tape 20 tends tobend excessively and it ceases to be possible to obtain a desired shape.If it is in excess of 50°, on the other hand, the edge parts becomeeasier to be chipped excessively.

Preferable work conditions according to this invention may be describedas follows:

Rotational speed of the semiconductor wafer: 500-2000 rpm; Feeding speedof abrading tape: 50-200 mm/min; Pressure on the pad: 5-20 N; Supplyrate of abrading liquid: 200-1000 ml/min.The semiconductor wafer 11, after having its outer peripheral partsabraded, is subjected to a back-grinding process, as shown in FIG. 3,such that its back surface is abraded by a rapidly rotating cup-shapedgrindstone such that a final thickness is obtained.

Next, the invention is described more in detail by way of test andcomparison examples. For this purpose, an apparatus as shown in FIG. 4was employed for abrading.

As shown in FIG. 4, the abrading apparatus according to the firstembodiment of this invention for outer peripheral parts of asemiconductor wafer mainly comprises a holding table 23 provided to astage 24 for carrying thereon a semiconductor wafer 11 horizontally withits back surface (to be abraded) facing upward, a rotating mechanism 21connected to a motor 32 for rotating this semiconductor wafer 11, and anabrading head 40 for abrading outer peripheral parts of thesemiconductor wafer.

The holding table 23 is in the shape of a porous plate and serves tohorizontally carry thereon the semiconductor wafer 11 in the shape of adisk. The semiconductor wafer 11 placed on the holding table 23 is keptthereon by a suction force through a suction pipe 28 connected to theholding table 23. The suction pipe 28 is connected to a suction pump(not shown) disposed externally.

The position of the center of rotation of the semiconductor wafer 11 onthe holding table 23 is made adjustable by detecting the outerperipheries of the semiconductor wafer 11 by a periphery sensor (alaser-type transmission detection sensor).

The abrading head 40 is disposed approximately perpendicularly to thesurface of the semiconductor wafer 11 such that the abrading tape can bepressed to the upper surface of the semiconductor wafer 11 while theupper part of the abrading head 40 is inclined in the forward directionby less than 10° from the vertical. In other words, when the upper partof the abrading head 40 is inclined towards the semiconductor wafer 11,it is preferable to make the angle of this inclination less than 10°.This is because the outer peripheral parts of the semiconductor waferbecome an obtuse angle if the outer peripheral parts are abraded withthe inclination less than 10° and the generation of chipping becomesrare. This is the same if the upper part of the abrading head 40 isinclined backward.

Semiconductor wafers with a surface (for forming semiconductor devices)protected by a protective sheet 12 as shown in FIG. 3A were used.

The rotating mechanism 21 is provided with a rotatable holding table 23and a motor 32 for rotating it. The holding table 23 is provided with avacuum chuck 22 for holding the semiconductor wafer 11 by suction. Afterthe semiconductor wafer 11 to be abraded is placed on the holding table23, it is kept in position by suction through a suction tube 28. Theholding table 23 is rendered rotatable by means of a bearing holder 25affixed to a stage 24 through a rotary shaft 27. For holding thesemiconductor wafer 11 by suction, the rotating mechanism 21 isconnected to an external suction pump through the suction tube 28passing inside the rotary shaft 27 and further through a rotary joint.The semiconductor wafer 11 is rotated by connecting a belt pulley 26 aaffixed to the rotary shaft 27 of the holding table 23 with another beltpulley 26 b affixed to the motor shaft 33 of the motor 32. The motor 32is affixed to the stage 24 through a support shaft 31.

The abrading head 40 is a box-shaped structure made of a plate 41 towhich the abrading tape 20 is mounted. The abrading head 40 isstructured such that the abrading tape 20 wound around a feed reel 42will be taken up by a take-up reel 43 by passing by an auxiliary roller45 a, a lower roller 44 a, an upper roller 44 b and another auxiliaryroller 45 b. Between the lower roller 44 a and the upper roller 44 balong the trajectory, the abrading tape 20 is pressed by a holding guide46 against the outer peripheral part of the semiconductor wafer 11 tocarry out the abrading process. The lower roller 44 a and the upperroller 44 b are adjusted such that the abrading tape 20 will be smoothlyguided towards the front surface of the semiconductor wafer 11 with anangle of inclination less than 10° from the vertical. The upper part ofthe abrading head 40 may be inclined either forward or backward. Aselection may be appropriately made according to the position of the tipof the outer peripheral parts of the semiconductor wafer 11 when theabrading process is carried out. In either case, the inclination shouldbe by 10° or less for the reason explained above.

In the running system of the abrading tape 20, tape tension adjustingrollers and auxiliary rollers may be added in any convenient manner.

The abrading tape 20 is pressed by a pad 47 at the tip of the holdingguide 46. A pressure adjusting cylinder 48 is connected through theholding guide 46 for adjusting the pressure.

This adjustment of pressure by the holding guide 46 may be effected by amechanism shown in FIG. 5, for example, by adjusting the pressure of airsent into an air tube 62 by means of a regulator 61 to a specified leveland moving the holding guide 46 by the pressure adjusting cylinder (aircylinder) 48. The pad 47 for pressing the back surface of the abradingtape 20 is attached to the tip of the holding guide 46 and is pressedagainst the outer peripheral part of the wafer together with theabrading tape 20 to carry out the abrading process.

It is preferable to use a pad 47 made of an elastic material withshore-A hardness in the range of 20-50°. A material such as resinfluorides (polytetrafluoro ethylene (PTFE) and tetrafluoroethylene-perfluoro alkylvinylether polymers (PFA)) with small frictionalresistance is preferable. It is also possible to coat the tip surface 63of the pad 47 (the contact surface with the abrading tape) with alubricant such that the vibrations of the contact portion can bediminished and the tape can be run smoothly and hence that thegeneration of chipping and defects on the semiconductor wafer can beprevented.

A abrading apparatus thus structured for outer peripheral parts of asemiconductor wafer serves to rotate the semiconductor wafer 11 placedon its holding table 23 and to form an abrading surface by running theabrading tape 20 provided to the abrading head 40 such that its slopewith respect to the front surface of the semiconductor wafer 11 is lessthan 10° from the vertical. The abrading tape 20 is advanced at aspecified speed.

The pressing position of the abrading tape 20 against the outerperipheral part of the semiconductor wafer 11 can be adjusted byproviding a pressing position adjusting mechanism as shown in FIGS. 7and 8. An outline of this adjusting mechanism and its operations will bepresented next with reference to FIGS. 7 and 8.

FIG. 7 is a schematic front view of the pressing position adjustingmechanism 69. FIG. 8A is a schematic side view of the pressing positionadjusting mechanism before it is pressed against the outer peripheralpart of a semiconductor wafer, and FIG. 8B is a schematic side view ofthe pressing position adjusting mechanism as it is pressed against theouter peripheral part of the semiconductor wafer.

As shown in FIGS. 7 and 8, the pressing position adjusting mechanism 69is provided inside the abrading head 40 and functions to swing so as torotate the holding guide 46, comprising a rotary arm 70 for holding theholding guide 46 with the pad 47 at its end between two planar members71 a and 71 b, a shaft 72 that penetrates and connects with the planarmembers 71 a and 71 b, a motor 74 connected to the shaft 72 and servingto generate a torque for rotating the rotary arm 70, and a gear head 73provided between the shaft 72 and the motor 74.

The planar members 71 a and 71 b of the rotary arm 70 further rotatablyhold the lower roller 44 a, the upper roller 44 b and the auxiliaryroller 45 a between them. The shaft 72 which penetrates the planarmembers 71 a and 71 b is a cylindrical member in the shape of a bar andis connected to the motor 74 through the gear head 73. As the shaft 72is rotated by the motion of the motor 74, the rotary arm 70 rotatesaround the shaft 72.

The gear head 73 serves to control the torque by varying the rotationalspeed of the motor 74 and to thereby control the rotational position ofthe rotary arm 70, or its swinging position. A stepping motor or aservomotor may be used as the motor 74.

The holding guide 46 is placed at a specified position of the rotary armsuch that the abrading tape 20 can abrade the outer peripheral part ofthe semiconductor wafer 11 by being pressed by the pad 47 and is held bybeing sandwiched between the planar members 71 a and 71 b. The pressureadjusting cylinder 48 for causing the holding guide 46 to slide isplaced on the back side of the holding guide 46.

As shown in FIG. 7A, the holding guide 46 and the abrading tape 20pressed by the holding guide 46 are placed at a position opposite theouter peripheral part of the semiconductor wafer 11 placed on thewafer-holding table (not shown).

Next, as shown in FIG. 7B, the shaft 72 is rotated by driving the motor74 and controlling the torque by means of the gear head 73. The rotationof the shaft 72 causes the rotary arm 70 to rotate around the shaft 72and the abrading tape 20 being compressed by the holding guide 46 comesto be pressed against the outer peripheral part of the semiconductorwafer 11 at a specified contact angle for carrying out the abrasionprocess.

Since the abrading position on the outer peripheral parts of thesemiconductor wafer 11 can be adjusted by means of the pressing positionadjusting mechanism 69, the accuracy of the abrasion process can beimproved by varying the angle and the pressure of compression by theabrading tape 20.

Next, the methods according to this invention will be explained by wayof examples. The abrading methods and conditions used in the followingtest and comparison examples are as follows.

Test Example 1

A protective sheet of about 8 inches (for example, adhesive tape P7180of a thermosetting type for protection of semiconductor surfacesproduced by Lintec Corporation) is adhesively attached to the surface ofa semiconductor wafer of 8 inches with semiconductor devices formedthereon. After its position was adjusted on the holding table of anabrading apparatus with its front surface facing downward, its positionwas fixed by suction.

The abrading tape 20 was of the type having epoxy resin applied to thesurface of a PET film as the binder resin and having carborundum (SiC)abrading particles of #600 attached thereto by the electrostaticspraying method and hardened by heating. This tape was mounted to theabrading head 40 for the process. A silicon sponge with shore-A hardness30° was used as the pad with Teflon (registered trademark) pasted as alubricant on the surface.

The conditions for the processing were as follows:

Rotary speed of the wafer: 1000 rpm; Feed speed of abrading tape: 100mm/min; Pressure on pad: 10 N; Supply rate of abrading liquid (purewater): 500 ml/min.The outer peripheral parts of semiconductor wafers were abraded togetherwith the protective sheet under these conditions.

Test Example 2

This was carried out under the same conditions as Test Example 1, exceptthat a #1000 tape produced by electrostatic spraying was used as theabrading tape.

Test Example 3

This was carried out under the same conditions as Test Example 1, exceptthat a #2000 tape produced by electrostatic spraying was used as theabrading tape.

Comparison Example 1

This was carried out under the same conditions as Test Example 1, exceptthat a tape produced by mixing #320 carborundum (SiC) and a binder resin(polyester), applying this mixture to the surface of a PET base film bya reverse roll coater, and drying was used as the abrading tape.

Comparison Example 2

This was carried out under the same conditions as Test Example 1, exceptthat a tape produced by mixing #600 carborundum (SiC) and a binder resin(polyester), applying this mixture to the surface of a PET base film bya reverse roll coater, and drying was used as the abrading tape.

Comparison Example 3

A grindstone comprising a diamond wheel with #1200 diamond abradingparticles combined by a resin was used instead of an abrading tape witha wafer edge grinding apparatus W-GM-4200 (tradename) produced by TokyoSeimitsu-sha. The conditions of the process were as follows:

Rotary speed of the wafer: 200 rpm; Rotary speed of the grindstone: 5000rpm; Depth of cutting: 50 μm/min (φ 100 μm/min); Supply rate of abradingliquid: 3 L/min.

Method of Evaluation

For the speed of processing, the changes in the diameter of the waferper unit time were measured by using a digital caliper (CD-45C(tradename) produced by Mitutoyo Corporation). Chipping was measured andobserved by using a device KP-2700/MX-1060Z (tradename) produced byHIROX Corporation. The abraded surface conditions were evaluated bymeans of a device EPRO212-EN (tradename) produced by Yuuhi Denshi-sha.

Results of Evaluation

The results of the evaluation carried out by the method described aboveare shown below in Table 1.

TABLE 1 Speed of Depth of processing chipping Abrading tape (φ mm/min)(μm) Clogging Test Electrostatic 0.85 5-7 Not present Example 1 spraying#600 Test Electrostatic 0.66 3-5 Not present Example 2 spraying #1000Test Electrostatic 0.57 3 or less Not present Example 3 spraying #2000Comparison Roll coating 0.68 20-30 Somewhat Example 1 #320 presentComparison Roll coating 0.40 15-20 Present Example 2 #600 ComparisonGrindstone 0.20 50 or greater Present Example 3 abrading #1200

The processed semiconductor wafers were evaluated regarding the speed ofprocessing, the depth of chipping and the condition of clogging, and thefollowing results were obtained.

By the method of Test Example 1, the processing speed was greater thanthe speed obtainable by traditional abrading methods using a diamondwheel, the depth of chipping was good at 5-7 μm, and no clogging wasobserved on the tape.

By Test Examples 2 and 3, the processing speed was somewhat reduced butthe chipping depths were respectively 3-5 μm and less than 3 μm, and noclogging was observed on the tapes.

With the tapes of the coated types of Comparison Examples 1 and 2, bycontrast, the processing speed was low and the chipping depths weresignificantly increased. This may be because the abrading capability isadversely affected by the clogging in the tapes.

With the diamond wheel used in Comparison Example 3, the abradingcapability was good in the beginning but the chipping soon increased asthe clogging took place gradually.

Although the invention has been described above as applied to theabrasion of outer peripheral parts of a semiconductor wafer, it goeswithout saying that the present invention is equally applicable to theabrasion of outer peripheral parts of other disk-shaped crystallinematerials such as silicon carbide, sapphire and potassium nitride.

1. A method of abrading outer peripheral parts of a semiconductor waferhaving a front surface on which semiconductor elements are formed and aprotective sheet is adhesively attached, said method comprising thesteps of: holding said semiconductor wafer such that said front surfaceis horizontal; and causing an abrading tape mounted inside an abradinghead to run and pressing said abrading tape against and thereby abradingan outer peripheral part of said semiconductor wafer; wherein saidabrading tape has abrading particles attached thereto by electrostaticspraying.
 2. The method of claim 1 wherein said semiconductor wafer isheld with said front surface facing downward and said outer peripheralpart is abraded together with said protective sheet.
 3. The method ofclaim 1 wherein said abrading tape runs horizontally or vertically whilebeing pressed against said outer peripheral part of said semiconductorwafer.
 4. The method of claim 1 wherein said abrading tape mountedinside said abrading head is pressed against and caused to abrade saidsemiconductor wafer, having a tape surface sloped by an angle of 10° orless from the vertical direction.
 5. The method of claim 1 wherein saidabrading particles are within the range of #600 or 30 μm to #3000 or 5μm.
 6. The method of claim 1 wherein a holding guide provided with a padat a tip is mounted inside said abrading head and wherein a slidingmotion of said holding guide causes said abrading tape to be pressedagainst and to thereby abrade said outer peripheral part of saidsemiconductor wafer.
 7. The method of claim 6 wherein said pad comprisesan elastic material having shore-A hardness in the range of 20-50°. 8.The method of claim 7 wherein said pad comprises a lubricant material atleast on a frontal contact surface.
 9. An abrading apparatus forabrading outer peripheral parts of a semiconductor wafer having a frontsurface on which semiconductor elements are formed and a protectivesheet is adhesively attached, said abrading apparatus comprising:holding means for holding said semiconductor wafer such that said frontsurface is horizontal; and an abrading head containing therein anabrading tape which is adapted to run and to abrade an outer peripheralpart of said semiconductor wafer being held by said holding means;wherein said abrading tape has abrading particles attached thereto byelectrostatic spraying.
 10. The abrading apparatus of claim 9 whereinsaid abrading head is rotatable such that said abrading tape runshorizontally or vertically while being pressed against said outerperipheral part of said semiconductor wafer.
 11. The abrading apparatusof claim 9 wherein said abrading head is rotatable such that saidabrading tape is pressed against and caused to abrade said semiconductorwafer, having a tape surface sloped by an angle of 10° or less from thevertical direction while running.
 12. The abrading apparatus of claim 9wherein said abrading particles are within the range of #600 or 30 μm to#3000 or 5 μm.
 13. The abrading apparatus of claim 9 wherein a holdingguide provided with a pad at a tip is mounted inside said abrading headand wherein a sliding motion of said holding guide causes said abradingtape to be pressed against and to thereby abrade said outer peripheralpart of said semiconductor wafer.
 14. The abrading apparatus of claim 13wherein said pad comprises an elastic material having shore-A hardnessin the range of 20-50°.
 15. The abrading apparatus of claim 14 whereinsaid pad comprises a lubricant material at least on a frontal contactsurface.
 16. The abrading apparatus of claim 13 wherein said abradinghead further comprises a pressing position adjusting mechanism thatrotates said holding guide in a radial direction of said semiconductorwafer; wherein said pressing position adjusting mechanism comprises arotary arm that undergoes a rotary motion with said holding guidemounted thereto, a shaft that is connected to said rotary arm and adriving device that is connected to and transmits a torque for saidrotary motion to said shaft; and wherein said abrading head serves tocontrol said torque by said driving device to adjust the rotary positionwhere said abrading tape is pressed by said holding guide onto saidouter peripheral part of said semiconductor wafer.